Apparatus for indicating the degree of supersaturation of boiling solutions



A. L. HOLVEN APPARATUS FOR INDICATING THE DEGREE OF Nov. 25, 1941.

SUPERSATURATION 0F 1301mm SOLUTIONS 3 Sheets-Sheet 1 7 Filed Sept. 12, 1938 INVENTOR. 36 MM Nub w Rut-ho as \AEQQW wow. .wi

1941- A. L. HOLVEN 7 4 APPARATUS FOR IND'ICATING THE DEGREEOF SUPERSATURAT-ION OF BOILING SOLUTIONS.

Filed Sept. 12, 1938 3 Sheets-Sheet-Z NOV. 25, 1941. I HOLVEN 7 2,263,847

- APPARATUS FOR INDICATING THE DEGREE 0F SUPERSATURATION OF BOILING SOLUTIONS Filed Sept.. 12, 1938 3 Sheets-Sheet 3 IN VEV TOR.

' Patent No. 2,135,511,

Patented Nov. 25, 1941 APPARATUS FOR INDICATING THE DEGREE OF SUPERSATURATION OF BOILING SO- LUTIONS Alfred L. Holven, Crockett, Calif. Application September 12, 1938, Serial No. 229,582 11 Claims. (Cl. 73 51) The present invention relates to improvements in apparatus for indicating the degree of supersaturation of a boiling solution and is a continuation in part of my copending application for patent, Serial No. 48,942, filed November 8, 1935,

entitled Method and apparatus for indicating the degree of supersaturation of a boiling solution. The apparatus contemplated by this disclosure is also adapted for use in the system of control which forms the subject matter of my copending application Serial No. 79,400ffiled May 12, 1936, Patent No. 2,135,512, entitled System of control for evaporating apparatu s.- Attention is here also directed to another copending application Serial No. 81,678, filed by me May 25, 1936, Patent No. 2,135,513, and entitled Method and apparatus for controlling the concentration of boiling solutions, which application broadly discloses and claims a system in which a variable resistance shunt is provided with a temperature responsive resistance to vary the efiect of the temperature responsive resistance upon the system in accordance with changes in purity of a'solution undergoing concentration.

The principal object of this invention is to provide an improved apparatus for obtaining a con'- tinuous measurement of the degree of supersaturation of boiling solutions.

A more specific object of the invention is to provide improved apparatus and circuits for obtaining a measurable value which is representative of the degree of supersaturation of a boiling solution and in which the measurable value is in the form of a potential difi'erence that is unafiected by variations in the absolute pressure under which the boiling of the solutiontakes place, and is proportional to the difference between the boiling point of water or other solvent and a fixed reference temperature.

Another object of the invention is to provide an improved means in apparatus of the above character which will compensate for the effect of variations in the purity of the boiling solution on the obtained measurement of the degree of supersaturation.

Other objects and advantages will be in part hereinafter pointed out and in part evident to those skilled in the art, as the description of the invention proceeds.

It is well known that in the crystallization of sucrose both the quantity and quality of sugar crystallized are dependent upon the maintenance of the proper degree of supersaturation in the solution at various ess. Therefore, the importance of providing means for the measurement of the degree of supersaturation of boiling solutions will be readily apparent to those skilled in the art, In other words, the provision of means for obtaining an accurate measure of the existing degrees of supersaturation of a boiling solution is of incalculable value. While the device tobe described in the subsequent pages is applicable in the crystal lization of practicallyv all materials, for the purpose of this description its adaptation to the crystallization of sugar will in particular be discussed.

In my prior application from which the subject matter of this application has been divided out it was disclosed that the degree of supersaturation of a boiling sugar solution is a function of the boiling point of the sugar solution and the absolute pressure in the evaporating pan and may be represented by a mathematical formula Tw-K T ,tan 0 wherein, as disclosed in my prior application, T10 and Ts are respectively the boiling points of water and a sugar solution at the same absolute pressure and K is a reference temperature, the value of which is determined by the point at which the constant supersaturation line of any given solution intersects the line representing a supersaturation coeflicient of zero, and in which tan 0 is the slope of a constant supersaturation line produced by plotting the boiling point of water against the boiling point of a sugarsolution "at the same absolute pressure.

In this prior application, it is further disclosed that electrical quantities corresponding respectively to the numerator Tw-K, and the denominator Ts-K could be produced by means of Wheatstone-bridge circuit arrangements and that by associating these circuits together in a suitable manner, an apparatus capable of providing a continuous measurement of the coefiicient of supersaturation would result, said measurement being unaflected by variations in either absolute pressure, boiling temperature, or purity of the sugar liquor;

In the development of this-method and means of measuring the degree of supersaturation of a boiling solution the'inventor has discovered, new and useful improvements in such apparatus. These improvements, form the subject matter of the present invention. It is to be clearly understages of the boiling procstood, however, that these improvements do not in any way detract from the value of the device for measuring supersaturation described in said prior application, as an accurate measure of the supersaturation of a boiling solution can be readily and accurately obtained with said prior apparatus. The present invention relates primarily to certain modifications and improvements on the apparatus of said prior disclosure which will simplify to a considerable extent the equipment formerly required to obtain the same result.

Essentially the improvements contemplated by this invention may be set forth as follows:

1. The use of a manometer arrangement of special design similar in principle to an absolute pressure gauge, as a substitute for the resistance thermometer and pilot pan arrangement described in the aforementioned application.

2. The substitution of a simplified apparatus for continuously compensating for the effect of variations in purity of the solution on the supersaturation values for the variable resistance and cam arrangement described in the prior application.

These improvements, as stated above. provide a simpler and more reliable means of measurement and compensation than that employed in the apparatus of the prior application. A brief discussion at this time will more clearly illustrate the advantages of the present invention.

In the apparatus described in my prior copending application, the electrical quantity representative of the difference between the boiling point of water and a reference temperature has been producedby mounting a resistance thermometer, that is connected in one arm of a Wheatstone bridge circuit, inside of a pilot pan in which water is boiling at the same absolute pressure as that of the boiling solution. This method, while satisfactory for all practical purposes, has proven unwieldy and expensive. Another difliculty is that the pilot pan must be carefully made and must be free of any external leakage.

Investigation has shown that with my previously described circuit arrangement a manometer of special design, to be hereinafter described,

may be substituted in lieu of the pilot pan. This manometer provides a much simpler and more compact means of producing an electrical quantity proportional to the difierence in temperature between the boiling temperature of water and a reference temperature. In this improved device the changes in the absolute pressure under which the solution is boiling in the vacuum pan will cause a column of mercury to fluctuate in a tube of predetermined design to such an extent that the variations in the resistance value of two resistance wires or electrodes contained thereinwill correspond identically with the variations produced by a resistance thermometer .in a pilot pan at corresponding absolute pressures. In this way resistance values may be obtained by the wires or electrodes in the manometer arrangement which will correspond at all times to those values which would be obtained by the resistance thermometer in the pilot pan under the same conditions of absolute pressure in the evaporating pan.

Referring now to another of these improvements, previously the means of compensating for changes in the purity of the boiling solution also appeared subject to certain limitations. The use of a cam arrangement for purity compensation, as disclosed in my prior application, required knowledge beforehand of the changes in purity which might take place during the bollina of a solution. This was necessary in order that the cam be designed to provide the proper compensation in accordance with the predetermined purity values. While such a device does effectively and automatically compensate for the variations in purity of the boiling solution, the necessity for previous data regarding such fluctuations in purity has certain disadvantages.

As a means to avoid these disadvantages it has been found that if the resistance of a thermometer located in the boiling solution is shunted by a high resistance, changes in the value of this high resistance shunt can be made that will modify the effective value of the resistance thermometer exactly in accordance with the efiect of purity on the slope of supersaturation lines. Such a result is obtained in accordance with the present invention by locating a pair of conductivity electrodes in the boiling solution and connecting these electrodes in series and in shunting relation with the thermometer as a substitute for the high resistance shunt. In this arrangement a continuous and automatic compensation for the effect of changes in the purity of the solution is obtained. This can be explained by the fact that an impure sugar solution con-' tains inorganic mineral salts and as the amount of these salts increases, the purity of the sugar solution decreases. Therefore, during boiling operations, as the purity drops, the amount of mineral ash will correspondingly increase and this in turn will decrease the resistance or, conversely, increase the conductivity of the solution between the two electrodes. The operation of this improved apparatus on the above basis will become more apparent as the details of these improvements are disclosed later in the specification.

, For a better understanding of the invention reference should be had to the accompanying drawings, wherein there is shown by way of 11- lustration, and not of limitation, preferred electrical circuits and apparatus by means of which the objects of the invention are obtained.

In these drawings:

Figure 1 schematically illustrates an improved arrangement by which a potential difference proportional to the difference between the boiling point of water or other solvent and a fixed reference temperature can be obtained.

Figure 2 is a schematic illustration of an improved arrangement for compensating for the effect of changes in the purity of a boiling solution on the degree of supersaturation.

Figure 3 is a graph showing the resistance values of the thermometer shunt which are required across the conductivity electrodes for sugar solutions" of different purities. v

Figure 4 is a composite diagram of the circuit features illustrated in Figures 1 and 2.

Figure 5 is a schematic and perspective diagram showing an improved mechanism by means of which supersaturation values of a boiling solution can be automatically measured and recorded and also the circuits and means by which automatic compensation for the variable factors are obtained. I

Reference is now made to Fig. l of thedrawings, wherein there is shown an arrangement employing an absolute pressure responsive device by means of which a potential difference corresponding to the numerator Tw-K of the aforementioned formula may .be obtained. As here shown, the arrangement contemplates the employment of a manometer 10 of special design having resistance forming electrodes II and I: that are adapted to be connected into one leg of a Wheatstone bridge circuit AECD that is excited by means of a battery B. As here shown, the resistance electrodes [I and I2 are inserted in the leg AE of the Wheatstone bridge circuit by means of conductors l3 and I4 Connected in the three remaining legs of the Wheatstone bridge circuit there are suitable resistances l5, l6 and H which are so chosen with respect to each other as to resistance value that the potential difference across the points D and E of the bridge circuit will be proportional to the expression Tw-K for any value of resistance that may be produced by the resistance electrodes II and I2 of the manometer device l0. As shown, the fixed resistance I5 is disposed in the leg AD of the Wheatstone bridge circuit, the fixed resistance I6 is disposed in the leg CD and the fixed resistance 11 is connected in the leg EC of the bridge circuit. In addition to the resistance electrodes II and I2 the leg AE of the Wheatstone bridge circuit includes avariable resistor l8 by means of which.

adjustments can be made to compensate and correct for inaccuracies that might be introduced into this circuit by reason of the length of the conductors I3 and I4 and/or other local conditions.

In order to vary the resistance value in the leg AE of the bridge circuit AECD, the resistance electrodes II and I2 are immersed in a column of mercury 19 which is supported in a curved and inclined tube Ml of special size and design, as will hereinafter appear. is sealed at its upper end and at its lower end it is shown as connected in sealed relation with the interior of a suitable mercury containing vessel 2| having an outlet conduit 22 that is adapted to be connected to and communicated with the interior of a vacuum boiling pan. With this arrangement it will be seen that as changes in absolute pressure take place within the container 2| the column of mercury within the curved tube 20 will be caused to rise and fall and thus short circuit more or less of the resistance electrodes H and I2 and. thus produce a resistance value present arrangement any increase in absolute pressure within the vacuum pan will cause the mercury I 9 to rise in the inclined tube 20 and thus act to short circuit increasing portions of the resistance electrodes II and I2 and thereby decrease the value of the resistance produced by these electrodes in the arm AE of the Wheatstone bridge circuit. To those familiar with the electrical art it is well known "that the potential difference produced in a Wheatstone bridge circuit of the type described will vary with any increase in the resistance of one arm. It is also known that a similar result may be obtained. by providing for a decrease in the resistance of an adjacent arm of the same bridge circuit. Therefore, as distinguished from my prior disclosure, instead of locating the resistance provided by the electrodes II and I2 in the arm AD of the bridge circuit and controlling this resistance by temperature thermometer responsive to changes in a pilot pan, in which water or other solvent is boiled at the same absolute pressure as that existing within the vacuum boiling pan, the resistance electrodes l l and I2 are substituted for the resistance thermometer and are located in the The inclined tube 2IJ- that will decrease as the absolute pressure in- 'equal to 45.4 ohms.

arm AE of the bridge circuit. This arrangement will produce the same results as in my former disclosure as the potential difference across the points D and E of the bridge circuit will vary identically in both arrangements with variations in the absolute pressure prevailing in the vacuum boiling pan. In order to obtain this identical variation, it is, of course, necessary that the inclined tube 20 be mathematically designed so that the rise, and fall of the mercury column l9 will i .provide exactly the proper change in resistance.

This will be determined by movements of the mercury column in the tube 20 and the resistance value per unit of length provided by the resistance electrodes II and I2.

For the purpose of clarity one typical calculation is presented, calculating first on the arrangement and apparatus disclosed in my prior application in which a variable resistance in the form of a resistance thermometer located in a pilot pan is located in the arm AD of the bridge circuit AECD. For the sake of simplicity a resistance value of 50 ohms will be assumed as the resistance of the unit in each arm of the bridge circuit AECD. Obviously, when all four resistance values are exactly equal, the potential difference across the points D and E will be zero.

Now assume that the water in the pilot pan is boiling at a temperature of 50 C. and that the resistance of the particular resistance thermometer employed increases from 50 ohms to 55 ohms at that temperature.- In such an event the potential difierence across the points D and E, in accordance with Wenners formula becomes:

= .024 volt Now, if the temperature responsive device is located in arm EA of the bridge AECD the necessary value which the resistance unit must assume at 50 C. to provide the same potential difference across the points D and E may be calculated as follows:

(50 X50) (E'A X50) (50 +1511) (50 +50) Solving this equation, EA becomes 45.4 ohms. This means that the manometer tube 20 must be so shaped and the resistance of the electrode wires II and I2 must be so chosen that an absolute pressure in the vacuum boiling pan corresponding to a water boiling temperature of 50 C. in a pilot pan will force the mercury l9 up into the tube 20 and short circuit the electrode wires l I and I2 to provide a resistance value exactly In this manner resistance values for other pilot pan temperatures can be obtained. A preferred design for the inclination and curvature of the tube 20 and which represents one embodiment of this invention is shown in Figure 1 of the drawings. It will be understood that other designs and shapes may be employed, depending upon the resistance of the wire used for the electrodes II and I2, without departing from the spirit and scope of the. invention.

As an alternative form of this invention, it will be understood that a device. operating on the Potential across= principle of a vacuum gauge may be substituted for ,the absolute pressure responsive manometer arrangement described above. In-such a vacuum responsive device the mercury column will short circuit the resistance electrodes H and I2 and will, of course, move in a reverse direction from that obtaining in the manometer device I!) described above and thus cause an increase in the amount of resistance provided by the electrode wires II and I2 as the vacuum increases. In the event that such a device is substituted, the resistance provided for by the electrodes II and I2 in the mercury column will be connected in the arm AD of the bridge circuit, as is the case where a resistance thermometer responsive to the temperature in a pilot pan is used as described in my prior application. In this latter arrangement, however, it should be pointed out that such a vacuum device will require compensation for fluctuations in the atmospheric pressure in order to secure an accuracy that will be comparable with the results obtainable with the absolute pressure manometer device hereinabove described, and therefore, the use of this alternative form is much less desirable.

Reference is now made to Fig. 2 of the drawings, wherein there is shown a Wheatstone bridge circuit and apparatus by means of which an electrical quantity corresponding to the denominator Ts-K of the aforementioned formula is obtained. The arrangement here illustrated is substantially similar to that employed in my earlier disclosure, except that the device employed to compensate for the effect on thesupersaturation values due tochanges in purity in the boiling solution is of my present improved form. As here shown, the numeral 23 designates a vacuum boiling pan of the type commonly used for crystallizing sugar solutions. At the top of the boiling pan 23 there is a conduit 24 that connects with a suitable vacuum producing A'ECD is properly designed and balanced and influenced by the resistance thermometer 21, it will, as stated above, produce a potential difference across the points E'D' of the bridge circuit that will be proportional to the expression Ts-K when the sugar solution has a purity corresponding to 100. In my prior application, to

apparatus such as a condenser and at the bottom of the pan 23 there is a discharge outlet 25 through which the concentrated solution may be discharged after the boiling operation or in other words, at the end of a strike as when a sugar solution is being concentrated. Within the vacuum pan 23 there is also provided a steam heating unit 23 for raising the solution within the pan 23 to the proper boiling temperature. Associated with the boiling pan 23 there is a Wheatstone bridge circuit A'E'C'D', and disposed within the boiling pan 23 there is a temperature responsive resistance thermometer 21 by means of which this bridge circuit may be influenced in response to temperature changes that take place in the boiling solution. The temperature responsive resistance thermometer 21 is shown as connected in the leg A'D' of the bridge circuit by conductors 28 and 29. In the other legs A'E, E'C and C'D' of the Wheatstone bridge circuit there are respectively resistances 3| 3| and 32. The leg AD of this bridge circuit also includes a fixed resistance 33 that is connected in series with the resistance thermometer 21. As a means for exciting this bridge circuit A'E'CD there is a battery B which is connected between the points A and C of the bridge circuit. At this point it should be stated that the relative values of the resistances 30, 3|, 32 and 33 are so chosen and adjusted with respect to each other that any potential diiference that may beestablished across points D'E will be proportional to the expression Ts-K for any value of response which the resistance thermometer 21 may assume, all as disclosed in my prior application.

With the above described arrangement it will be understood that when the bridge circuit compensate for the changes in purity of the solution undergoing concentration there is provided variable resistances that operate in series with the potentiometer winding by means of which the degree of saturation is obtained. As distinguished from that prior arrangement, my present invention contemplates the elimination of such a variable resistance and the substitution of means to correct for the efiects of purity upon the value Ts-K, which is automatically controlled directly by the conductivity of the boiling solution.

It has been found that in lieu of shortening the effective length of the supersaturation measuring potentiometer slidewire to compensate for changes in the purity ot'the solution, as taught in my prior disclosure, it is possible to obtain the same compensation by shunting the resistance thermometer 21 in the vacuum pan. While this may be accomplished by the use of a manually adjustable resistance shunt of high value a continuous and automatic compensation for the effect of purity may be obtained by introducing a portion of the solution undergoing boiling as a conductivity shunt across the terminals of the resistance thermometer 21. In such an arrangement two electrodes having a connection with the resistance thermometerterminals are introduced into the boiling solution at a properly spaced distance apart so that a portion of the liquid will provide a conductive path between the electrodes as will hereinafter appear. When two suchelectrodes are thus provided, the resistance or conductivity produced by the interposed boiling solution will vary in accordance with changes in the purity of solution and thereby provide for an automatic compensation of this variable.

In its preferred form this apparatus contemplates the use of two spaced conductivity electrodes 34 and 35 the space between which is connected in shunt with the resistance thermometer 21 by means of conductors 36 and 31. The conductivity electrodes 34 and 35 are shown as suspended within an inverted bell or other suitable inverted structure 38 into which a sample portion of the solution undergoing concentration can be periodically drawn to thus produce what might be termed a conductivity shunt, the value of which will be determined by the purity of the solution, across the terminals of the resistance thermometer 21. As shown the electrodes 34 and 35 are suspended in insulated relation so as to depend downwardly into the bell 38 and at the lower end of this bell 38 there is a screen 39 that functions to prevent the accumulation of sugar crystals upon the electrodes 34 and 35. At the top of the bell 38 there is a conduit 40 that is adapted to be alternately connected to a suction or pressure producing means at periodic intervals. For this purpose the conduit 40 is ilmagnetic solenoid 45 which will be periodically energized as will hereinafter appear.

With this arrangement it will be readily seen that when the apparatus is in operation the resistance theremometer 21 will provide a resistance value comparable to the temperature of the boiling solution and thus influence the bridge circuit A E C D in the manner above described- At the same time when the valve ll is in the position shown in this figure of the drawings, a portion of the solution undergoing concentration will be drawn upwardly into the bell 38 and as a result a shunting conductivity resistance will be bridged across the terminals of the resistance thermometer 21 and thus modify the efiect thereoi as determined by the purity of the solution within the boiling pan. At periodic intervals, as will hereinafter appear, the position of the valve piston 44 will change to shut off the vacuum and admit air under pressure to the bell 38 and thus force the solution within the bell through the screen 39 to clean the same and thus prevent the accumulation of crystallized sugar either upon the conductivity electrodes 34 and 35 or the screen 39'.

The application of this principle of compensation for changes in purity of the solution undergoing concentration is based on the well known fact that the conductivity of a sugar solution varies in accordance with the concentration of inorganic mineral salts present in the solution. Pure sugar solutions (100 purity) contain no impurities or mineral matter, while the impure or low period solutions are high in mineral matter. Therefore, the concentration of this mineral matter or salts can be relied upon as indica-- tive of the purity of the solution. Therefore, if the two conductivity electrodes 34 and 35 are properly designed a shunting resistance of the required resistance value for the sugar solution at various purities can be automatically introduced into the shunt circuit of the resistance thermometer 21. Such a conductivity shuntwill act to control the resistance eifect of the thermometer 21 upon the bridge circuit A E C D' so that a proper supersaturation value for the particular purity of solution will be recorded.

As explained in my prior disclosure, the slopes of the lines representative of the tangent 0 values corresponding to their respective degree of supersaturation are affected by the purity of the solution and change the measurement of the degree of supersaturation being made. Thus, for every purity of sugar liquor there is a set of tangent 0 values with which definite supersaturation coeflicients correspond. However, since the majority of refined sugar liquors boiled in the pan 23 are high in purity, the supersaturation recording instrument is normally calibrated for solutions having a purityof 100, therefore, if a. solution of lower purity is being boiled or if the purity of the liquor should drop during the boiling of a strike of sugar, it will be'clear that a calibration of the instrument for a purity of 100 would not be accurate for a solution of lower purity as, for example, a liquor having a tion under these conditions would be 1.55 or 0.15 toohigh. As stated above in my prior disclosure compensation for the effect of such a change in purity on the supersaturation reading was obtained byshortening the efiect of length of, the potentiometer slidewire by introducing a second variable resistance in series therewith across the points D E of the bridge circuit A E C D. This variable resistance was automatically controlled by a cam arrangement of predetermined design so as to introduce a value of resistance which would result in an indication of the proper supersaturation value of 1.4 instead of the value 1.55. In the present proved means of compensating for the effect of purity, instead of this variable resistance and the cam arrangement for controlling same, it has been .found simpler to modify the eflect of resistance of the resistance thermometer 21 by the use of the conductive shunt, as described above in connection with Fig. 2 of the drawings, to thus secure a proper indication of the degree of supersaturation.

Carrying the above example further, inspection of similar graphs for 100 purity sugar liquor shows that the temperature of a solution boiling at 4 inches absolute pressure and having a supersaturation of 1.4 is 605 C. Therefore, the value of the conductive shunt which must be introduced in the thermometer circuit to secure the proper compensation must be such as to cause the eflective temperature of the vacuum pan thermometer 21 to be reduced from|-61.8 C. to 60.5 C. In other words, if a standard 50 ohm resistance thermometer is employed when the temperature is 613 C. its resistance will be 57.6 ohms. In order that the proper supersaturation be indicated with such a. thermometer its effective resistance must be reduced to 57.32 ohms as the equivalent of the temperature 605 C.

It is now assumed that the conductivity circuit, which includes the solution in the inverted bell 38 and shunts the vacuum pan thermometer 21, is designed'so that the resistance between the two electrodes 34 and 35 when immersed in 100 purity liquor is 50,000 ohms. Such a high resistance shunt across the resistance thermometer 21 will obviously have no appreciable effect on the supersaturation value read when the liquor is of 100 purity, However, when the degree of supersaturation is to be measured on a purity liquor the resistance across the electrodes 34 and 35 will be decreased correspondingly as previously explained. This will'cause the eflective resistance of the resistance thermometer circuit to decrease to a value of 57.32 ohms and thus cause the apparatus to record and respond to the proper value of 1.4 for the 90 purity liquor. And as a result compensation for this change in purity will be automatically obtained without recalibrating the instrument.

Calculations for, the required shunt resistance- The resistance of the shunting conductivity cell must, therefore, be 9500 ohms in order to give the proper supersaturation reading for a 90 purity liquor. Similar values of resistance have been calculated for liquors of other purities and these values have'been plotted as shown in Fig. 3. In this plot, the resistance values of the shunt for sugar liquors ranging from 60 to 100 purity are plotted with the purity of the liquor set up as' ordinates and the required resistance of the shunt appears as the abscissae.

Reference is now made to Fig. 4 of the drawings, wherein the manometer l and its bridge circuit AECD is shown as associated with the bridge circuit AEC'D that is associated with the vacuum boiling pan 23 as described above in connection with Fig. 2 of the drawings. In this figure of the drawings, the. manometer bridge circuit AECD and the vacuum boiling pan bridge circuit AE'C'D' are each shown as excited from a common source of electrical potential in the form of a battery B2. It will be noted that in this arrangement where one side of the battery B; connects to the bridge circuits, there are inserted at the points C and C slide wire resistances 46 and 41 having sliding contacts 48 and 49 respectively. These resistances 46 and 41 with their Sliding contacts 46 and 49 provide means by which compensation may be made for the fact that each supersaturation line has its own reference temperature or point of intersection with the zero supersaturation line, as explained above. By a simultaneous and equal movement of the sliding contacts 48 and 49over their respective resistances 46 and 41, as will hereinafter appear, the relative resistances of the two adjacent arms of each of the two Wheatstone bridge circuits will be changed by the amounts required to compensate accurately for such deviation from the intersection point as is characteristic of the particular supersaturation being measured. It will be noted that the points E and E of the two above described bridge circuits are connected together, and connected between these points and the point D of the vacuum pan bridge circuit, there is a suitable slide wireresistance 50. Associated with the slide wire resistance 50 there is an adjustable contact that is connected through a galvanometer 52 to the point D of the manometer bridge circuit by means of a conductor 53.

- At this point it should be noted that the galvanometer 52 is shown as having a protective shunting circuit which includes a switch 54 that is to be described in more detail hereinafter. In addition to the temperature responsive thermometer 21 and the means of correcting for purity which includes the conductivity electrodes 34 and 35, this circuit also shows a variable resistor 55 as connected in the circuit of the electrode 34. The purpose of this variable resistor 55 is to permit of adjustments in the circuit after the apparatus has been installed and can, of course, be relied upon at any time where a correction or compensation may be required in this purity responsive shunting circuit.

In the composite circuit thus formed, the electrical potential existing between the points D and E of the bridge circuit AECD, is proportional to the numerator Tw-K and the electrical potential between the points D and E of the bridge circuit A'ECD', bears-the same proportionality to the denominator Ts-K. Now if the sliding contact 5| is moved along the slide wire resistance 56 to a point where the galvanometer 52 gives a balanced reading, that proportion of the total resistance in the circuit ED' which is in the galvanometer circuit will be a direct measure of the tan 0 value or slope of the constant supersaturation line for the particular liquor being boiled. 'I'herefore, when the slide wire resistance 50' is properly calibrated it is possible to read directly therefrom the supersaturation value of the boiling solution, as explained in the above mentioned prior application.

In Fig. 5 of the drawings, the composite or multi-bridge circuit of Fig. 4 is shown as associated wth an automatic measuring and recording mechanism of the type illustrated and described in United States patent to Leeds, No. 1,125,699, dated January 19, 1915. The bridge balancing mechanism described in this patent is old and well known in the art and therefore a detailed description of its mode of operation is thought unnecessary. It will be suflicient for the purpose of the present description to state that the mechanism described by this prior patent comprises a continuously rotating constant speed motor 56 that is adapted to drive a shaft 51 and through a suitable worm and worm gear system 58, a recording chart 59 with which a tracing pen or print wheel cooperates. Disposed at a right angle to the shaft 51 and terminating adjacent one end, there is a second shaft 6| that has a frictional driving disc 62 with which pivotally mounted friction shoes 63 are adapted to cooperate when pressure is exerted thereupon by either one of two cams 64 and 65 which are carried by the motor driven shaft 51. The pivotally mounted friction shoes 63 are suspended upon a delicately mounted lever system that is adapted to be set in operation by a pointer or arm 66 which is moved by potential responsive winding 61 of the galvanometer 52. A cam 66 which is carried by the shaft 51 also operates in conjunction with the friction shoe supporting leverage, as will be well understood from the description of this apparatus given in the above referred to,Leeds patent.

In this adaptation of the above identified automatic bridge balancing mechanism, there is provided upon the shaft 6| a suitable insulating drum 69 about which the slide wire resistances 46,

41 and 50 are disposed, and for the purpose of v controlling the movement of a tracing pen. 10 there is also provided a pulley II about which is looped a continuous belt 12 that carries the tracing pen I0. With this arrangement it will be understood that the drum 69 will be rotated intermittently backward and forward as the galvanometer pointer 66 is deflected in one direction or another in response to an unbalance of the potential in the bridge system connected therewith.

The manner in which the conductivity cell 38 that provides compensation for changes in the purity of the boiling solution and which includes the conductivity electrodes 34 and 35 is rendered operative and periodically cleaned as suggested above will now be described. As here illustrated,

-the shaft 51 which isdriven by the constant 43 and thus permit air under pressure to be blown therethrough to thus discharge the sugar solution therefrom,.and at the same time clean the screen 39 at the end thereof. The frequency with which the switch 14 is operated and the duration thereof is controlled by the speed of the cam 13 and the length of a raised surface 16 thereupon. As shown, the cam 13 is adapted to be driven at a relatively slow speed through a worm gear drive 16 that connects with the shaft 51 and a bevel gear drive 18 that connects with a shaft 19 upon which the cam 13 is mounted.

In order to render the galvanometer device inoperative during the period when the control switch 14 is closed and to also protect the galvanometer winding 61 against shock due to sudden changes in the condition, the cam 13 is also shown as adapted to substantially simultaneously close a second switch 80 that is connected by means of conductors 8| and 82 to form a short circuit around the winding 61 of the galvanometer 52. After the cam I3 has thus operated to close the switches 14 and 80 and the circuits have been restored to normal, it will be understood that the piston valve 44 will assume its original position, as shown in Figs. 2 and 4 of the drawings, to permit the admission of a fresh quantity of the boiling solution into the bell 38 where it will cooperate with the conductivity electrodes 34 and 35 to introduce the proper correction for purity in the boiling pan- Wheatstone bridge circuit A'E'CD'. At this point it may be added that since the galvanometer under normal operating conditions is in a balanced condition the closing of the switch 80 will not cause any radical movement of the galvanometer winding 61.

A specific example illustrating how the coefficient of supersaturation is measured by the combined action of the various components of the above described apparatus is believed unnecessary as this should be clearly understood by reference to the prior application. However, from the foregoing description it will be evident that this invention offers a distinctly novel improvement in method and means for measuring the degree of supersaturation of a boiling sugar solution. Furthermore, it should be obvious that such measurement is accomplished by a system whose accuracy is unaffected by changes in boiling temperature, absolute pressure, or purity of the sugar solution being boiled.

In connection with the improved apparatus illustrated, it should be understood that this invention is not limited to the exact arrangement shown. It should be apparent that there are ways in which the circuits and associated apparatus could be arranged to operate in a different manner and still accomplish the same results. The specific form shown represents the preferred embodiment of the invention, but it is obvious that the novel principles fully disclosed herein may lead those skilled in the arts to other means and fields of application without departing from the scope of this invention. It is, therefore, to be clearly understood that I do not limit myself to what is specifically shown in the drawings or described in the specifications, but as this invention is' broadly new, it is desired to claim it as such so that all changes that come within the scope of the appended claims are to be considered as part of this invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is 1. .In a system for electrically determining the degree of supersaturation of a boiling solution,

the combination of an electrical temperature responsive circuit adapted to produce a potential representative of the temperature of a boiling solution, a second electrical circuit responsive to the absolute pressure under which the solution is boiling, means associated with each of said electrical circuits for introducing a voltage change in produce a potential representative of the absolute pressure in the solution boiling pan, means associated with each of said electrical circuits for introducing a voltage change in the potentialsproduced thereby which change is determined by the supersaturation of the boiling solution, means connected between said electrical temperature responsive circuits responsive to the ratio between the resulting potentials to indicate the degree of supersaturation of the boiling solution, and means including a conductive path through a portion of the solution being boiled for introducing an additional change in said potentials dependent upon the purity of the solution.

3. In a system for indicating the degree of supersaturation of a boiling solution, the combination of a vacuum pan in whichthe solution under control is boiled, a manometer device responsive to the absolute pressure existing in said vacuum pan, a resistance adapted to be controlled by said manometer device, said vacuum pan and said manometer device being operative at the same degree of absolute pressure, a thermosensitive bridge circuit associated with said vacuum pan adapted to produce a potential proportional to the difference between the temperature existing within said vacuum pan and a reference temperature dependent upon the supersaturation and purity of the solution, a second bridge circuit associated with said manometer device and its controlled resistance adapted to produce a potential dependent upon the absolute pressure existing in the vacuum pan, means associated with said bridge circuits for determining the ratio between the potentials produced thereby, and means responsive to said last means for indicating the degree of supersaturation ofthe solution boiling in said vacuum pan.

4. In a system for determining the degree of supersaturation of a boiling solution, the combination of a vacuum pan in which the solution under control is boiled, a resistance controlling manometer connected to said vacuum pan, said vacuum pan and said manometer being operative at the same degree of absolute pressure, a thermosensitive bridge circuit associated with said vacuum pan adapted to produce a potential proportional to the difference between the temperature existing within said vacuum pan and a reference temperature dependent upon the supersaturation and purity of the solution, a

second bridge circuit associated with said manometer adapted to produce a potential proportional to the absolute pressure-existing within of a boiling pan, a resistance thermometer lo-,

cated within said boiling pan and connected in said bridge circuit to control the potential produced thereby, and means comprising a pair of electrodes immersed in the boiling solution and forming a high resistance shunting circuit across the terminals of said resistance thermometer,

whereby the conductivity of said solution due toimpurities therein will automatically compensate for errors introduced in the potential produced by said bridge circuit due to impurities in said boiling solution.

6. In a system for controlling the supersaturation of a boiling solution employing a potential producing bridge circuit of the character described, the combination of a boiling pan adapted to contain a solution undergoing concentration, an inverted bell disposed in said solution, means for exhausting the air from said bell to permit a filling of the same with the solution, and a pair of current conducting electrodes disposed in spaced insulated relation within said bell and having connections with said bridge circuit, whereby a controlling resistance change will be introduced into said bridge circuit dependent upon the presence of impurities in said solution.

'7. In apparatus of the character described for determining the supersaturation of a boiling solution, the combination of a vacuum pan in which a solution is boiled, a pair of spaced and insulated electrodes adapted to form the terminals of a. conductance path through a portion of the boiling solution within said vacuum pan, an electrical measuring circuit connected with said electrodes and adapted to be influenced by the conductance and/or resistance characteristics of the solution undergoing boiling, and means for periodically causing said electrodes to be immersed in the boiling solution, whereby renewed portions of said boiling solution will be introduced into the circuit between said electrodes durin the boiling operation.

8. In apparatus of the character described for determining the supersaturation of a boiling solution, the combination of a vacuum pan in which a solution is boiled, an inverted bell-like structure disposed within said pan and located beneath the surface of the boiling solution, a pair of spaced and insulated electrodes suspended within said bell-like structure and adapted to form the terminals of an electrical circuit through a portion of the boiling solution when the solution is drawn up into said bell-like struc-- ture, an electrical measuring circuit connected with said electrodes and adapted to be influenced by the conductance and/or resistance characteristics of the solution undergoing boiling, means connecting the interior of said bell-like structure with a vacuum producing means, whereby a portion of the boiling solution will be drawn thereinto, and means for controlling the connection between said vacuum producing means and said bell-like structure, whereby renewed portions of said boiling solution will be periodically drawn up into said bell-like structure during a boiling operation.

9. In apparatus'of the character described for determining the supersaturation of a boiling solution, the combination of a vacuum pan in which a solution is boiled, an inverted bell-like structure disposed within said pan and located beneath the surface of the boiling solution, a pair of spaced and insulated electrodes suspended within said bell-like structure and adapted to form the terminals of an electrical circuit through a portion of the boiling solution when the solution is drawn up into said bell-like structure, an electrical measuring circuit connected with said electrodes and adapted to be influenced by the conductance and/or resistance characteristics of the solution undergoing boiling, means connecting the interior of said bell-like structure with a vacuum producing means whereby a portion of the boiling solution will be drawn thereinto, means connecting the interior of said bell-like structure with a positive air pressure producing means for forcing the boiling solution out of said bell-like structure, and means for alternately controlling the connections between said vacuum producing means and said positive air pressure producing means whereby renewed portions of said boiling solution will be periodically drawn up into and discharged from said bell-like structure during a boiling operation.

10. In apparatus for determining the supersaturation of a boiling solution, the combination of a vacuum pan in which a solution is boiled, an electrical measuring circuit having a resistance thermometer adapted to control the response of said measuring circuit as the temperature of the boiling solution varies, a pair of spaced electrodes disposed within said vacuum pan and forming the terminals of an electrical circuit through a portion of the boiling solution, said spaced electrodes being connected to the terminals of said resistance thermometer to include said portion of the boiling solution as a shunting circuit therefor, whereby the effective controlling influence of said resistance thermometer upon said electrical measuring circuit will be varied by changes in the purity of the solution undergoing boiling.

11. In a system of the character described, employing a thermosensitive bridge circuit adapted to produce a potential depending upon the temperature of a boiling solution, the combination of a boiling pan, a resistance thermometer located in said boiling pan and connected in said bridge circuit to control the potential produced thereby, and means including a portion of the boiling solution forming a current conducting path through the solution in shunt circuit with the terminals of said resistance thermometer, whereby any change in the conductivity of said boiling solution due to impurities therein will operate to provide a compensating resistance change in the resistance thermometer connection with said bridge circuit. 4

ALFRED L. HOLVEN. 

